二、单项选择（共15小题；每小题1分，满分15分）
从每小题所给的A、B、C、D四个选项中选出一个最佳选项，把其编号填入答题卷相对应的空格内。
1. This is _______ empty bottle but it is _______ useful one.
A. a, a B. an, a C. a, an D. a, the
2.－ What about going out for a walk with me? － Not _______ I finish my dinner.
A. as B. when C. after D. until
